The API of the DM is documented in de installation directory. Using this API you can add the attributes to the entities.
There are several examples of transformation script on OTN.
you can find a transformation script here: https://community.oracle.com/message/10109948#10109948
In this example there is a jdbc connection which you can replace with the reading of the excel file. And you have to replace the coding to work on entities.
Hope that helps.